Wet spinning of acrylonitrile polymers



U, 1955 J. M. TERPAY 2,716,586

WET SPINNING OF ACRYLONITRILE POLYMERS Filed Sept. 8, 1951 JOH/V- M. TERPA) ATTUR E) United States Patent WET SPINNING or ACRYLONITRILE Poms/mus iohn M. Terpay, Cleveland, Ohio, assignor to Industrial Rayon Corporation, Cleveland, Ohio, a corporation of Delaware Application September 8, 1951, Serial No. 245,697

Claims. (Cl. 18-54) This invention relates to the production of fibers from acrylonitrile polymers and copolymers by the wet-spinning method. More particularly, this invention is concerned with a process employing aqueous baths for the coagulation of ethylene carbonate-type spinning solutions of such polymers.

An important factor in the commercial success of a wet-spinning process for producing acrylonitrile polymer fibers is the selection of the coagulating bath. A highly advantageous selection would involve one which could satisfy, among others, the following conditions: (a) a bath made with low cost coagulant components; (b) a bath which could be continuously regenerated with facility and high efficiency, particularly as to the recovery and recycling of the solvent component therein for reuse in making a spinning solution; and (c) a bath capable of successful and continuous spinning and of producing suitable fibers under normal-type operating conditions, e. g. temperature, yarn speed, equipment, etc.

Aqueous-type baths provide an answer to condition (a) because of their relatively lower material cost. As to condition (b) calling for high efiiciency in the used-bath reclamation operation, the most desirable situation would appear to be an aqueous bath comprising a minimum number of coagulant components so as to minimize the number of separation steps and the extent of treatment necessary to recover and recycle the polymer solvent. Accordingly, an aqueous bath which can be handled and treated during the recovery operation as an essentially two-component bath system, i. e., water and solvent, and which, in addition, can tolerate a substantial accumulation of solvent in the bath without adversely affecting the spinning operation thereby minimizing the quantity of used bath required to be regenerated to maintain the desired bath proportions, would provide the optimum situation. In such a two-component system, the polymer solvent could be recovered from a minimum quantity of used bath and recycled substantially directly after only one separation step, i. e., the evaporation of water from the used bath.

The achievement of successful water-bath spinning of acrylonitrile polymer fibers is itself, however, a difiicult goal without also including the above desirable objectives. This achievement, however, is made increasingly difiicult by the employment of an ethylene carbonate-type spinning solution, i. e., a spinning solution containing ethylene carbonate as the polymer solvent. Among other things this difiiculty is due to the relatively high boiling point 238 C. of the ethylene carbonate solvent and its easily hydrolyzable and relatively unstable nature. This solvent cannot be subjected to excessive reclamation treatments, e. g., numerous separation steps, high temperatures, and other conditions tending to promote hydrolysis or transesterification such as, for example, those caused by the presence of inorganic salts.

Various methods have been proposed heretofore for the employment of aqueous-type baths for the coagulation of various acrylonitrile polymer spinning solutions.

2,716,586 Patented Aug. 30, 1955 "ice The operating conditions employed in these proposals, however, do not provide the desired objectives previously mentioned. Thus, it has been proposed to incorporate into water baths various inorganic salts such as calcium chloride, zinc chloride, sodium thiosulfate, etc. and also organic compounds for the purpose of achieving successful water-bath spinning. Such water bath proposals provide neither the facility nor the efiiciency desired for solvent reclamation. This is due in a large part to the nature of the materials incorporated in the bath and to the excessive solvent reclamation steps required by the presence of such materials. In another aqueous-bath proposal employing spinning solutions containing inorganic salts as polymer solvents, e. g., calcium thiocyanate, etc., successful water-bath spinning is said to be achieved by maintaining very low bath temperatures, i. e., below 10 C. and preferably, about 0 C. Methods employing exceedingly 10w bath temperatures are not considered desirable because of the inherent operational difficulties presented such as, for example, the additional refrigeration cost required and the exceedingly low spinning speeds in such low temperature operations.

However, it has been discovered as a result of the present invention that successful water-bath spinning can be achieved with ethylene carbonate-type spinning solution which is capable of producing fibers possessing high strength, soft hand and suitable dyeing properties.

Further, aqueous-bath spinning conditions have been discovered under which successful spinning can be achieved with a water bath consisting essentially of only two components, i. e., water and solvent. Moreover, these spinning conditions permit normal-type operations particularly as to spinning temperatures, yarn speeds, and equipment.

in accordance with the present invention, this may be accomplished by forming a spinning solution of acrylonitrile polymers and copolymers containing in the polymer molecule at least about by weight of acrylonitrile, such spinning solution comprising the acrylonitrile polymer, ethylene carbonate as a solvent, and water in an amount between about 2.5% and 18.5% by weight. This spinning solution is extruded through a spinneret into a coagulating liquid comprising water and between about 10% and 50% by weight of ethylene carbonate, and the total of the water and the ethylene carbonate in the coagulating liquid comprising at least about by weight thereof. Preferably, the cloud point of the spinning solution should be below about 65 C.

The polymeric spinning solutions of the present invention, as previously stated, contain water, in an amount between about 2.5% and 18.5% by Weight, in combination with the ethylene carbonate and the acrylonitrile polymer. Particular advantages, however, are derived when the water in the spinning solution is maintained at between about 10% and 15%. In general, when employing a polymeric material in which the acrylonitrile content approaches it is found advantageous to maintain the water concentration in the spinning solution at between about 12% and 15% by weight.

In making up the spinning solution containing the Water additive, it is found advantageous to employ polymer solids at a concentration of between about 8% and 30% by weight and preferably, between about 12% and 18% solids, the balance of the spinning solution, with advantage, consisting essentially of ethylene carbonate and water. If desired, small amounts, i. e., less than about 8% by weight, of polyhydric alcohol compounds, e. g., ethylene glycol, propylene glycol, dipropylene glycol, etc., may also be incorporated in the spinning solution of the present process. This procedure for incorporating such materials is the subject of the H. A. Bruson and T. W.

3 Riener application Serial No. 105,910, filed I uly 9, 1949, issued June 24, 1952, as U. S. Patent No. 2,601,254.

The temperature of the spinning solution may be maintained with advantage between about 40 and 80 C. and preferably, between about 50 and 75 C. Maintaining these spinning solutions at temperatures above 80 C. for extended periods of time, e. g., by storing for periods of one-half hour or more, preparatory to extrusion, is not considered desirable in view of the accelerated rate of hydrolysis of the ethylene carbonate taking place at such higher temperatures. In general, it is found advantageous to store the bulk of the heated spinning solution at the lower temperatures and heat to the extrusion temperature only that small portion in transit to the spinneret. By this method, the elevated temperatures are maintained for only a short period of time for a relatively small amount of material. Where the above procedure is followed, extrusion temperatures, or more specifically, spinneret ternperatures above about 80 C. may be employed, if desired, without excessive decomposition of ethylene carbonate.

As previously indicated, in practicing the present process, some flexibility is available for varying the relative proportions of each of the components of the spinning solution, i. e., water content, solids content, molecular weight, etc., to suit the particular needs or desires. The extent of such flexibility is, however, controlled by the initial interrelationships that exist between these factors. These interrelationships must be considered in achieving the desired total effect, namely, successful spinning.

The combined effect of these variable factors is best expressed by what is termed herein as the cloud point of a given water-containing spinning solution prepared within the general limits previously described. The cloud point as defined herein is an expression in terms of temperature which characterizes the spinnability for a given spinning solution under the aqueous-bath conditions specified in the process. In general, it is the point of change from a cloudy or turbid solution to a clear, transparent solution. To achieve successful spinning under the waterbath conditions of the present process, the cloud point of the water-containing spinning solutions should be below about 65 C. With advantage, the cloud point of the spinning solutions should be between about and 65 C., and preferably between about and 55 C.

It is found advantageous to maintain a spinning solution at a temperature higher than its cloud point such as, for example, 5 or more. Thus, for example, a spinning solution containing 10% water, 78% ethylene carbonate, and 12% of a polymer having a molecular weight of about 45,000, has a cloud point between about and C. Accordingly, this formulation calls for an extrusion temperature of at least about to C. and preferably, 50 to 60 C. A similar spinning solution containing 15% water and 14% polymer has a cloud point between about and C., thus calling for an extrusion temperature of at least about C. and preferably, about C.

The coagulating liquid into which such spinning solutions are extruded comprises water and between about 10% and 50% by weight of ethylene carbonate measured at a distance within three inches from the spinneret, andadvantageously between about 10% and 40%. The total of the water and the ethylene carbonate comprises at least about 95% by weight of the bath liquid. Further, it is found particularly advantageous to employ coagulating baths consisting essentially of water and ethylene carbonate. If desired, however, relatively small amounts of other compounds, preferably organic compounds, may also be present in the bath provided, of course, that they do not amount to more than about 5% by weight of the coagulating bath, and further, that they do not other wise adversely affect the efficiency of the process. In general, the materials which can be tolerated in the water baths of the present process are those which are not harmful to the spinning operation and do not have to be separated from the reclaimed solvent by an additional recovery step at a later stage. Briefly, such additives may be characterized as those which are compatible with the solvent and do not materially reduce its solvent power when present in the solvent in concentrations up to about 8% by weight of the solvent, and in addition, which do not render it necessary to handle and treat the used bath as a three-component system rather than as a two-component system during the bath recovery and reclamation treatments.

Among such tolerable additives may be mentioned, for example, glycol compounds, e. g., ethylene glycol, dipropylene glycol, etc. Thus, for example, such compounds may be initially incorporated into the spinning solution in amounts up to about 8% for any desired purpose and then permitted to accumulate in the water bath at concentrations of not more than about 5% by weight of the bath. For example, when extruding spinning solutions containing about 6% of dipropylene glycol into water baths maintained at about 20% ethylene carbonate, the resultant concentration of dipropylene glycol in the bath would be about 1.5%, whereas with a bath maintained at about 35% ethylene carbonate, the concentration of dipropylene glycol therein would be about 2.8%. Such baths are treated as if they were two-component systems, i. e., solvent and water. Thus, the solvent recovery operation is performed in one major step, i. e., by evaporating the water from the used bath and recycling the solvent together with the glycol for re-use as polymer solvent. With regard to the ethylene carbonate content of the bath, particularly advantageous results are achieved when the concentration thereof in the bath is maintained between about 20% and 30% by weight of the coagulating bath.

During extrusion, the aqueous coagulating medium may be maintained with advantage at a temperature between about 45 and C; Ifdesired, or if found necessary, temperatures below or above this range may be employed provided, however, that difiiculties such as poor coagula tion, usually occurring at the lower temperatures, and excessive hydrolysis and decomposition of the ethylene carbonate, usually occurring at the higher temperatures, are successfully avoided. When employing spinning solutions at extrusion temperatures between about 70 and 80 C., it is found advantageous to maintain a lower bath temperature such as, for example, about 5 or more below that of the extrusion temperature. Coagulants between 50" and 75 C. are particularly advantageous.

The resulting formed fibers after removal from thecoagulating liquid may then be subjected to one or more stretching operations, and thereafter if desired, may be heat treated in a relaxed condition. The resulting product may be collected as a continuous filament yarn or it may be crimped and cut into staple fiber.

The invention will be further described in connection with the accompanying drawing which illustrates generally the process of the present invention.

A spinning solution is extruded through a suitable spinneret 11 immersed in an aqueous coagulating bath liquid 12 contained in a trough 13. The freshly formed thread 15 is withdrawn from the bath 12 and conducted to a roller 16. The roller 16 may be a thread-advancing device, and thus, if desired, a further aqueous treating liquid may be applied to the thread on the roller 16 by means of a delivery tube 18. The thread 15 discharged from the roller 16 is conducted to a succeeding roller 19 similar to roller 16 but operating at a greater peripheral speed, thereby imparting an air stretch to the thread between the rollers. If desired, treating or washing liquid, e. g., water, may be applied to the thread on the roller 19 by means of a delivery tube 20. The thread 15 from the roller 19 is then conducted through a stretching chamber 22 containing a heated aqueous medium24 entering the chamber through tube 25 and leaving through tube 26. The heated medium 24 may be an aqueous liquid, e. g., water, above about 80 C. or it may be steam. The thread withdrawn from the chamber 22 is then conducted to a succeeding roller 28 also similar to roller 16 and operating at a greater peripheral speed than the roller 19, thereby stretching the thread between the roller 19 and the roller 28.

The thread 15 from the roller 28 is conducted through a heated aqueous medium 29 contained in a trough 30 and thereafter conducted to a roller 32, also similar to roller 16 and operating at a lower peripheral speed than the roller 23, thereby causing the thread 15 to relax between the roller 28 and the roller 32. The heated medium 29 may be an aqueous liquid, e. g., water, above about 80 C., and preferably closer to 100 C. If de sired, an aqueous washing liquid, e. g., water with or without dispersed oleaginous materials, may be applied to the thread on the roller 32 by means of a delivery tube 33. The thread 15 from the roller 32 may be conducted directly to a thread-collecting device 37 and wound thereby as a package on a bobbin 38, or if desired, the thread may be conducted first to an internally heated, thread-advancing device having a progressively dimin ishing periphery in the direction of thread advance and thereafter collected by the device 37. Advancing device 35 may be employed both to dry and, if desired, to heat treat under relaxed tension at temperatures higher than 100 C.

This invention will be more fully described by the following examples, although it is understood that the invention is not intended to be limited by these examples. In these examples parts and percent of materials is intended to mean parts and percent by weight.

Example I 14 parts of polyacrylonitrile having an average molecular weight of about 47,000 is dissolved in 51 parts of ethylene carbonate and the resulting solution is then filtered and deaerated. To this solution is added a mixture of 20 parts of ethylene carbonate and 15 parts of water. The resulting solution having a cloud point of about 55 C. is heated to 70 C. and extruded at a rate of about 200 grams per minute through a spinneret having 412 holes (0.003 inch diameter) into a coagulating bath containing 75 parts of water and 25 parts of ethylene carbonate. The bath temperature is maintained at about 60 C. while the freshly formed filaments are drawn through the bath for a distance of about 48 inches. The thread is withdrawn from the bath at a rate of about 9.3 meters per minute and passed over two positivelydriven rolls positioned outside of the baths, the first roll being driven at a linear velocity of 9.3 meters per minute and the second roll at 44.5 meters per minute, thereby airstretching the yarn 4.8 times. The yarn is then drawn through a stretching bath containing water and about 13% of accumulated ethylene carbonate at a temperature of about 100 C. for a distance of about 25 inches and thereby given an additional stretch of 1.64 times resulting in an over-all stretch of about 7.7 times. The stretched thread is then passed under relaxed tension through a substantially all water bath at about 90 C. for a distance of about 25 inches. The resulting relaxed thread is collected at a rate of about 66 meters per minute and thereafter dried. The final product is a colorless, white thread having a tenacity of about 3.3 grams per denier and an elongation at break of about 18%.

Example II of about 20 C. is heated to 50 C. and. extruded at a rate of about 19 grams per minute through a spinneret having 40 holes (0.003 inch diameter) into a coagulating bath containing parts of water and 20 parts of ethylene carbonate. The bath temperature is maintained at about 65 C. while the freshly formed filaments are drawn through the bath for a distance of about 40 inches. The thread is withdrawn from the bath at a rate of about 41 meters per minute and passed over a positivelydriven thread-advancing device on which it is washed with a stream of water at 60 C. delivered at the rate of about 60 cubic centimeters per minute. The washed thread leaving the thread-advancing device is passed through a tube in which it is brought into direct contact with a jet of steam and stretched about ten times. The resulting stretched thread is then relaxed and dried at a rate of about 400 meters per minute on a tapered thread-advancing device internally heated to about 135-l45 C. The final product is a colorless white thread having a tenacity of about 2.3 grams per denier and an elongation at break of about 10%.

Example 111 12 parts of a copolymer containing acrylonitrile and 5% of 2-vinylpyridine having an average molecular weight of about 45,000 is dissolved in 48 parts of ethylene carbonate and the resulting solution is filtered and deaerated. To this solution is added a mixture of 30 parts of ethylene carbonate and 10 parts of water to yield a spinning solution having a cloud point of about 23 C. The resulting solution is then heated to 70 C. and extruded at the rate of about 35 grams per minute through a spinneret having 412 holes (0.003 inch diameter) into a coagulating bath containing 80 parts of water and 20 parts of ethylene carbonate. The bath temperature is maintained at about 60 C. while the freshly formed filaments are drawn through the bath for a distance of about 55 inches. The thread is then withdrawn from the bath at a rate of about 8.8 meters per minute by means of a driven roll positioned above the bath and then passed over a second similar roll, driven at a sufliciently higher peripheral speed to effect an air stretch between the rolls of about 2.95 times. The thread is then drawn through a stretching bath consisting of water and about l3% of accumulated ethylene carbonate at a temperature of about C. for a distance of about 20 inches. The thread in this bath is given an additional stretch of 2.73 times resulting in an overall stretch of about eight times. The stretched thread is then passed under relaxed tension through a bath consisting of water at about 80 C. for a distance of about 20 inches. The resulting thread is continuously collected at about 62 meters per minute and thereafter washed and dried. The resulting white thread has a tenacity of about 2.8 grams per denier and an elongation at break of about 18%. The dried yarn is then crimped and cut into staple lengths.

Example IV The procedure and conditions of this. example were the same as Example Ill except that the washed and dried thread is passed through an aqueous liquid containing 0.05% of an oleaginous yarn finishing agent to a tapered internally heated thread-advancing device which has a uniform decrease in periphery at a rate of about 9% for each 17.5 meters of yarn stored thereon. Steam at pounds per square inch gauge pressure is introduced and circulated in the device. The resulting thread is then collected at a rate of about 77 meters per minute and has a tenacity of about 3.1 grams per denier and an elongation at break of about 17% and a free shrinkage in boiling water of 12%.

Example V 14 parts of polyacrylonitrile having an average molecular weight of about 45,000 is dissolved in a mixture of 50 parts of ethylene carbonate and 6 parts of dipropylene glycol and the resulting solution is then filtered and deaerated. To this solution, there is added a mixture of 20 parts of ethylene carbonate and 10 parts of water. The resulting solution having a cloud point of about 46 C. is heated to 55 C. and extruded at a rate of about 66 grams per minute through a spinneret having 412 holes (0.003 inch diameter) into a coagulating bath consisting initially of about 70% water and 30% ethylene carbonate. The bath temperature is maintained at about 60 C. while the freshly formed filaments are drawn through the bath for a distance of about 55 inches. By maintaining the ethylene carbonate content in the bath at about 30%, the dipropylene glycol accumulates therein to a maximum of about 3 the balance being about 64% water. The thread withdrawn from the coagulating bath is processed according to the procedure of Example I, to yield a final product similar to the product of Example I.

The portions of the coagulating bath liquid which are continuously removed from the bath to maintain the ethylene carbonate content at 30% are processed as follows: The bath liquid is subjected to a flash distillation under sub-atmospheric pressure so as to remove the water present therein. The residual mixture of ethylene carbonate and dipropylene glycol is then treated with decolorizing carbon, filtered and recycled directly for use as solvent in the preparation of additional quantities of spinning solution.

The spinning solution cloud point values which are referred to in the examples, and which were previously characterized as indices of good spinnability, are determined in the following manner. A solution containing the desired proportions of polymer, ethylene carbonate and water is heated until a clear, transparent solution is obtained. The resulting solution is then permitted to cool slowly, with stirring, until the first signs of cloudiness appear. The temperature at which this change takes place is termed the cloud point. When employing solutions having a cloud point between about 20 and 65, the turbidity or cloudiness in the solution at the cloud point temperature is believed to be a precipitation of the polymer from the solution, whereas with solutions which are still clear and non-turbid at about 20 C., the turbidity or cloudiness which appears upon further cooling may be the precipitation of the polymer component or it may be a freezing or crystallization of the solvent component and more likely a combination of both. In determining the cloud point, it is particularly important that the solution be cooled slowly. Accordingly, when making cloud point determinations, a

cooling medium should be employed which is about 5 C.

less than the temperature of the solution being cooled.

As previously indicated this invention may be practiced under a variety of spinning solution conditions which are, of course, within the general limits hereinbefore described. Among the variables already mentioned in this connection are polymer solids content, water content, molecular weight of the polymer and a choice of homopolymer or copolymer. In addition, one may select a variety of thread deniers as the final yarn product, i. e., thread deniers as low as 75 to 100 up to heavy denier tows for staple. The process is found particularly useful in making the heavy denier type, i. e. over 500 denier and up to 3,000 or more. Moreover, these denier can be produced at low speeds or more advantageously, at higher speeds ranging from 30 meters per minute or higher. However, in selecting a given set of conditions as the operating conditions, and particularly when these changes involve changes in thread denier, spinneret hole size and spinning speed, it is found advantageous to determine preliminarily the most successful ratio of the extrusion speed of the spinning solution to the withdrawal speed of the thread from the coagulating bath. Thus, for example, when employing a spinning solution containing 12% polymer solids and water and withdrawing at the rate of about to meters'per minute, the extrusionrto-withdrawal ratio is advantageously maintained greater than about 1.3' to 1. In general, as the withdrawal speeds are increased to about 45 to 55 meters per minute, the extrusion-to-withdrawal ratio is decreased. Thus, under such conditions one can employ with advantage an extrusion-to-withdrawal ratio greater than about 1 to 1.

As previously mentioned, the formed fibers after withdrawal from the coagulating bath may then be subjected to a stretching operation, the amount of stretch varying from about 3 to 10 times or more as desired. Particular advantages however, are derived in this process by imparting total stretches of between about 6.5 and 10 times. The stretching operation may be accomplished in the presence of hot aqueous media such as, for example, in a stretching bath consisting essentially of water at about 100 C. or at higher temperatures, e. g., in steam or in higher boiling-point aqueous baths containing organic or inorganc compounds. Advantageously, the stretching operation may be accomplished in two steps, the first, an air stretch immediately after leaving the coagulating bath, and the second, in a hot aqueous stretching bath, e. g., a water bath at a temperature above about C. and preferably about 100 C. and above. Alternatively, as illustrated in the examples, the thread which is withdrawn from the coagulating bath may with advantage be preliminarily washed or rinsed with water to remove solvent therefrom and thereafter, stretched at temperatures of 100 C. or over, e. g., in steam. In general, more stretch can be obtained at the higher stretch temperatures.

The resulting stretched thread thereafter may be collected directly in package form and subsequently relaxed or, if desired, the relaxing operation may be performed immediately after the stretching operation in a continuous manner. For example, the stretched thread may be relaxed in hot aqueous media, e. g., water, steam, etc. at'temperatures above about 80 C. and preferably 100 C. or above. If desired, the relaxing operation may be combined with greater advantage with a treatment on an internally heated roll at the higher temperatures, e. g., on a tapered, thread-advancing reel or pair of threadadvancing drums into which heated fluid such as steam under pressure is circulated.

As previously stated, the proportion of acrylonitrile in the polymer molecule should be at least about 80% by weight and more advantageously, at least about by weight. A minor proportion of one or more vinyl compounds can be copolymerized with the acrylonitrile, for example: vinyl esters (vinyl acetate, vinyl formate, vinyl benzoate), vinyl ethers, and vinyl ketones; acrylic acid and its esters and amides; methacrylic acid and its esters, amides, and nitrile; maleic, itaconic, fumaric, crotonic acids and their esters, amides and nitriles; allyl alcohol and its esters and ethers; styrene and nuclear substituted styrenes, e. g. chloroand dichloro-styrene; halogenated monoethylenic compounds such as vinyl chloride, vinyl fluoride, vinylidene chloride, 1,2-dichloro-propene-1, 1,2- dichloro-propene-2, allyl chloride, methallyl chloride, 2-chloro-allyl alcohol, and l-allyloxy-3-chloro-2-propanol; N-vinyl compounds such as N-vinyl pyrrolidone, N-vinyl succinimide, N-vinyl carbazole, N-tertiary butyl acryl-" amide, N-tertiary octyl acrylamide; 2- or 4-vinylpyridine; and the like.

The acrylonitrile polymers may be prepared by any suitable polymerization method such as, for example, polymerization with oxygen-yielding catalysts, e. g., benzoyl peroxide, hydrogen peroxide, tertiary butyl hydroperoxide, potassium or ammonium persulfate, etc. Redox polymerization systems employing oxygen-yielding catalysts such as the above in combination with reducing agents such as sodium bisulfite, sodium hydrosulfite, sodium formaldehyde sulfoxylate, etc., may be used with advantage. Generally, after completion of the polymerization reaction, the resulting polymer is washed with water to remove any remaining impurities, and preferably, distilled or demineralized water is employed so as to achieve a minimum of impurities in the final polymer.

The molecular weights of the polymeric materials are preferably within the range of 10,000 and 250,000, or even higher, although copolymers having molecular weights between 30,000 and 100,000 may be used with particular advantage in the production of fibers.

The spinning solutions employed in the process of the present invention may be prepared by various methods. Thus, for example, one may prepare a room-temperature slurry of the polymer, ethylene carbonate and water and thereafter heat the slurry to effect dissolution of the polymer. Advantageously, the spinning solution may be prepared by first preparing a polymer solution without the water comprising ethylene carbonate and between about and of the polymer solids, deaerating this solution and then making the final spinning solution by adding the desired quantity of water in the form of a waterethylene carbonate mixture.

As previously indicated, the ethylene carbonate may be recovered from those portions of the coagulating bath liquid which are continuously removed from the bath to iaintain the desired water-ethylene carbonate ratio. The recovery operation involves evaporating the water from the bath portion and then recycling the residuum comprising substantially ethylene carbonate for use as solvent in the preparation of additional quantities of spinning solution. if desired, the ethylene carbonate may be treated with decolorizing carbon and filtered prior to its re-use in the preparation of additional spinning solution.

I claim:

1. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight and a polymer of acrylonitrile containing in the polymer molecule at least about 80% by Weight of acrylonitrile; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 50% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95 by weight thereof.

2. A method according to claim 1 in which the spinning solution has a cloud point below about 65 C.

3. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5 and 18.5% by weight and between about 8% and by weight of a polymer of acrylo nitrile containing in the polymer molecule at least about 80% by Weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95% by Weight thereof.

4. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight and a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95% by weight thereof.

5. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight and a polymer of acrylonitrile containing in the polymer molecule at least about by weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; extruding the resulting spinning solution into a coagulating liquid consisting essentially of water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight.

6. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by weight and between about 8% and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; extruding the resulting spinning solution into a coagulating liquid com prising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 20% and 30% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about by weight thereof.

7. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5 and 18.5% by weight and between about 8% and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; extruding the resulting spinning solution into a coagulating liquid consisting essentially of water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 20% and 30% by weight.

8. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by Weight and between about 8% and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; maintaining said spinning solution between about 40 and 80 C.; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95% by weight thereof.

9. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount be tween about 2.5% and 18.5% by weight and between about 8% and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by Weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; maintaining said spinning solution between about 40 and 80 C.; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95% by weight thereof; maintaining said coagulating liquid between about 45 and 80 C.

10. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 10% and 15% by weight and between about 12% and 18% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 90% by Weight of acrylonitrile, said spinning solution having a cloud point below about 65 C.; maintaining said spinning solution between about 50 and 75 C.; extruding the resulting spinning solution into a coagulating liquid consisting essentially of water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 20% and by weight; maintaining said coagulating liquid between about 50 and 75 C.

11. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, water in an amount between about 2.5% and 18.5% by Weight and between about 8% and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point between about 15 and 65 C.; maintaining said spinning solution between about and 80 C.; extruding the resulting spinning solution into a coagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about 95% by weight thereof; maintaining said coagulating liquid between about and 80 C.; stretching the resulting fiber in the presence of an aqueous medium at a temperature above about 80 C.

12. A method according to claim 11 in which the stretching operation is performed in the presence of steam.

13. A method according to claim 11 in which the 12 stretchingo'perati'on is performed in a bath comprising Water;

14. The method of forming an acrylonitrile polymer fiber comprising the steps, forming a spinning solution comprising ethylene carbonate, Water in an amount between about 2.5% and 18.5% by Weight and between about 8 and 30% by weight of a polymer of acrylonitrile containing in the polymer molecule at least about 80% by weight of acrylonitrile, said spinning solution having a cloud point between about 20 and C.; maintaining said spinning solution between about 40 and C.; extruding the resulting spinning solution into acoagulating liquid comprising water and ethylene carbonate; maintaining the ethylene carbonate concentration in said coagulating liquid between about 10% and 40% by weight, and the total of the water and the ethylene carbonate in said coagulating liquid comprising at least about by weight thereof; maintaining said coagulating liquid-between about 45 and 80 C.; stretching the resulting fiber in the presence of an aqueous medium at a'temperature above about 80 C.; heating the resulting stretched fiber under relaxed tension at a temperature above about 80 C.

15. A method according to claim 14- in which the relaxing operation is performed in a bath comprising water. I

References Cited in the file of this patent UNITED STATES PATENTS 2,558,733 Cresswell et al July 3, 1951 2,570,200 Bruson Oct. 9, 1951 2,570,257 McFarren Oct. 9, 1951 2,577,763 Hoxie Dec. 11, 1951 

1. THE METHOD OF FORMING AN ACRYLONITRILE POLYMER FIBER COMPRISING THE STEPS, FORMING A SPINNING SOLUTION COMPRISING ETHYLENE CARBONATE, WATER IN AN AMOUNT BETWEEN ABOUT 2.5% AND 18.5% BY WEIGHT AND A POLYMER OF ACRYLONITRILE CONTAINING IN THE POLYMER MOLECULE AT LEAST ABOUT 80% BY WEIGHT OF ACRYLONITRILE; EXTRUDING THE RESULTING SPINNING SOLUTION INTO A COAGULATING LIQUID COMPRISING WATER AND ETHYLENE CARBONATE; MAINTAINING THE ETHYLENE CARBONATE CONCENTRATION IN SAID COAGULATING LIQUID BETWEEN ABOUT 10% AND 50% BY WEIGHT, AND THE TOTAL OF THE WATER AND THE ETHYLENE CARBONATE IN SAID COAGULATING LIQUID COMPRISING AT LEAST ABOUT 95% BY WEIGHT THEREOF. 